Tissue products containing deliquescent materials and non-ionic surfactants

ABSTRACT

Tissue products, such as facial tissue, bath tissue, paper towels, table napkins and the like can be improved by incorporating a sufficient amount of a deliquescent material and a non-ionic surfactant into the product. The deliquescent material is capable of maintaining a very high equilibrium amount of water in the product which can be advantageous in preventing the products from drying out and improving hand feel. The non-ionic surfactant improves the ability to incorporate the deliquescent materials into the tissue products quickly during manufacture and can help control the equilibrium moisture content of the product.

BACKGROUND OF THE INVENTION

Tissue products, such as facial tissue, toilet paper, table napkins,paper towels and the like, generally have a very low moisture content ofabout 5 percent or less. While it is known to add humectants to tissueproducts to absorb moisture and improve the hand feel, humectants do notabsorb appreciable quantities of water relative to their weight. Hence,very large amounts of the humectant material are required to absorbmoisture in amounts sufficient to be effective. In addition, humectantmaterials do not form solutions with the water but rather exist aswater/humectant complexes. Hence the water is bound to the humectantmaterial and does not impart the same effect as free water in the sheet.Further, if the humectant material is a solid particulate, it willremain as a solid particulate in the sheet and can impart a gritty feel.

In commonly-assigned co-pending patent application Ser. No. 10/808,744,filed Mar. 24, 2004, by Shannon et al., it is disclosed thatdeliquescent materials can be incorporated into tissue products toprovide a high equilibrium moisture content and improved feel. However,it has since been discovered that producing such products can bedifficult at the high speeds associated with commercial tissue makingequipment because concentrated deliquescent salt solutions are notquickly transferred to the sheet and/or quickly absorbed into the sheet.This reduces the amount of the deliquescent material in the sheet andadversely impacts the properties of the final product.

Therefore, there is a need for a means to produce tissue productscontaining deliquescent materials and having a high, more easilycontrolled equilibrium moisture content and for a better means ofproducing such products at the high speeds associated with commercialtissue manufacturing operations.

SUMMARY OF THE INVENTION

It has now been discovered that aqueous solutions having a sufficientlyhigh concentration of deliquescent salts, in particular deliquescentinorganic salts, can be incorporated into tissue product sheets at highspeeds so as to impart a noticeable wet feel to the product. Inparticular, it has been determined that combining a non-ionic surfactantwith the deliquescent salt solution reduces the surface tension of thesolution sufficiently to enable the deliquescent salt solution to bequickly absorbed by the tissue sheet. Furthermore, it has beendiscovered that the non-ionic surfactant can be used to control theequilibrium moisture content of the sheet and thereby optimize thetactile sheet properties insuring that the sheet has sufficient moistureto provide a significant improvement in handfeel, yet does not give theappearance of a wet tissue sheet. In addition, certain non-ionicsurfactants are capable of providing improved feel characteristics tothe sheet by themselves, thus making the use of such materialsparticularly advantageous.

Hence, in one aspect the invention resides in a tissue productcomprising a tissue sheet containing a deliquescent salt and a non-ionicsurfactant, said tissue sheet having an equilibrium moisture content offrom about 10 to about 30 percent, more specifically from about 10 toabout 25 percent and still more specifically from about 15 to about 25percent. It has been determined that for equilibrium moisture contentsabove about 30 percent, the tissue product feels too wet, while forequilibrium moisture contents below about 10 percent, the increasedmoisture is not appreciably noticeable to the user.

In another aspect, the invention resides in a method for treating atissue sheet comprising: (a) providing a dry tissue sheet; (b) preparinga surfactant/deliquescent salt solution containing about 0.0001 dryweight percent or greater of a non-ionic surfactant and from about 20 toabout 80 dry weight percent of a deliquescent salt; and (c) topicallyapplying the surfactant/deliquescent salt solution to the tissue sheet,wherein the equilibrium moisture content of the tissue sheet isincreased.

(As used herein, the weight-percent of the deliquescent salt refers tothe weight percent of the non-hydrated salt. For example, whenCaCl₂.6H₂0 is used, the concentration refers only to the CaCl₂ portionand not the absorbed water.)

As used herein, a “deliquescent salt” is any salt that exists as a solidat a temperature of 30° C. or less when said material is dried to aroundfive percent or less moisture, said dry solid being capable of absorbinga sufficient amount of moisture from the air to form a solution.Specifically, such conditions for water absorption and solutionformation are met when the deliquescent material is exposed toconditioning at 50% relative humidity and a temperature of 23° C.±1° C.While any deliquescent salt can be used for purposes of this invention,particularly suitable deliquescent salts certain inorganic salts andtheir hydrates such as, but not limited to, calcium chloride, calciumchloride dihydrate, calcium chloride hexahydrate, magnesium chloride,magnesium chloride dihydrate, magnesium chloride hexahydrate, lithiumchloride, sodium acetate, potassium acetate and ammonium acetate. Aparticularly suitable organic salt is trimethylamine n-oxide.

As used herein, the “equilibrium moisture content” is the moisturecontent of a tissue sheet at 50% relative humidity and 23° C.±1° C.(standard TAPPI conditions). At equilibrium, the amount of moisturewithin the sheet will not change with time at the same humiditycondition. The equilibrium moisture content is expressed as a weightpercent of the dry sheet including the deliquescent salt and anyadditional non-volatile components. More specifically, the dry tissuesheet should be conditioned at least 4 hours at the TAPPI standardconditions prior to determining the equilibrium moisture content of thesheet. The equilibrium moisture content in the sheet can be controlledby the absorbent capacity of the sheet, the amount of water on a percentbasis that the deliquescent salt absorbs and the amount of thedeliquescent salt in the sheet.

The effectiveness of the surfactant/deliquescent salt solution added tothe tissue sheet can be characterized by providing a Single Water DropTest value (hereinafter described) of about 12 seconds or less, morespecifically about 8 seconds or less, more specifically about 6 secondsor less, more specifically about 4 seconds or less, and still morespecifically about 1 second or less. Consequently, thesurfactant/deliquescent salt solution can be advantageously applied totissue sheets traveling at machine speeds of about 100 feet or greaterper minute, more specifically from about 200 to about 8000 feet perminute, more specifically from about 200 to about 5000 feet per minute.

The surfactant/deliquescent salt solution can be incorporated into thetissue sheet by any suitable means known in the art, such as spraying orprinting. The add-on amount of the surfactant/deliquescent salt solutionthat is applied to the tissue sheet can be any amount sufficient toincrease the equilibrium moisture content of the tissue sheet to whichit is applied and will depend on the concentration of the deliquescentsalt, the concentration of the non-ionic surfactant, the desiredequilibrium moisture content, the particular deliquescent salt or saltsin the solution, etc.

It is found that in the absence of the non-ionic surfactant, theconcentration of the salt solution does have an impact on the ability ofthe sheet to rapidly absorb the salt solution. In particular,concentrated salt solutions are found to be much more slowly absorbedthan dilute solutions. On the other hand, it will be readily apparent tothose skilled in the tissue making art that being able to applysolutions having a high solids concentration to the web can beadvantageous in that the need to transfer less material can allow highermachine speeds to be achieved, there are fewer issues with web handlingand there is less of a need to dry/condition the product in order toobtain the desired moisture level in the final product. Accordingly, forpurposes herein, the amount of the deliquescent salt in thesurfactant/deliquescent salt solution can be from about 20 to about 80dry weight percent, more specifically from about 25 to about 70 dryweight percent, and still more specifically from about 30 to about 70dry weight percent.

The amount of the non-ionic surfactant(s) in the surfactant/deliquescentsalt solution for the purpose of providing the desired rapid absorptioninto the tissue sheet will depend upon factors such as the HLB value ofthe non-ionic surfactant, the structure of the surfactant, its criticalmicelle concentration and the concentration of the salt solution.Typically, the amount of the non-ionic surfactant(s) in thesurfactant/deliquescent salt solution will be about 0.0001 dry weightpercent of the total solution weight or greater, more specifically fromabout 0.0001 to about 1 dry weight percent of the total solution weight,more specifically from about 0.001 to about 0.5 dry weight percent ofthe total solution weight, and still more specifically from about 0.005to about 0.1 dry weight percent of the total solution weight. It isoften desirable to keep the surfactant concentration below the criticalmicelle concentration so as to reduce the level of foaming associatedwith the application of the solution. At times, however, it may bebeneficial to use substantially higher amounts of the non-ionicsurfactant, such as from about 0.5 to about 30 dry weight percent. Thiswill be the case when the surfactant is also capable of impartingadditional improvement to the handfeel of the product. For example, highmolecular weight polyether polysiloxanes, amino-functional polyetherpolysiloxanes and alkyl ethoxylates are found to improve the handfeel oftissue products. The amounts of these materials added to thesurfactant/deliquescent salt solution can be controlled in order tooptimize both the equilibrium moisture content and the surface feel ofthe tissue sheet.

The amount of deliquescent material residing in the tissue sheets of theproducts of this invention can be any amount that provides the desiredequilibrium moisture content. More specifically, the amount can be fromabout 2 to about 40 percent by weight of dry fiber or greater, morespecifically from about 3 to about 30 dry weight percent, morespecifically from about 4 to about 25 dry weight percent, and still morespecifically from about 5 to about 20 dry weight percent. The specificamount of the deliquescent material in the tissue sheet will depend uponthe desired equilibrium moisture content in the sheet, the specificdeliquescent material selected, the temperature of application of thesurfactant/deliquescent salt solution to the tissue sheet and thesolubility of the particular deliquescent salt at the applicationtemperature. Solutions having a high deliquescent salt concentration arepreferred because such solutions, when applied to the tissue sheet, willnot require additional drying of the tissue after they are applied. In apreferred embodiment, the surfactant/deliquescent salt solution is asaturated salt solution or one very near the saturation concentration.

The amount of the non-ionic surfactant residing in the tissue sheets ofthe products of this invention can be from about 0.00002 to about 3weight percent based on dry fiber in the sheet, more specifically fromabout 0.00005 to about 3 weight percent, more specifically from about0.00005 to about 2 weight percent, more specifically from about 0.0001to about 1 weight percent, and still more specifically from about 0.0001to about 3 weight percent.

Any non-ionic surfactant can be used provided it gives the desiredeffect. The lack of charge is an important feature of these surfactantsbecause ionic surfactants will undergo ion exchange reactions with thedeliquescent salts and typically will form insoluble precipitates suchthat the surfactants are rendered useless. On other occasions, the ionexchange reaction causes the deliquescent material to lose itsdeliquescent properties. Particularly preferred non-ionic surfactantsare water-soluble surfactants having a solubility greater than 0.02percent in the surfactant/deliquescent salt solution at a temperature of25° C. Other preferred water-soluble surfactants are those having, inparticular, a Hydrophilic-Lipophilic Balance (HLB) number of 4 orgreater, more specifically from about 4 to about 24, more specificallyfrom about 4 to about 20, and still more specifically from about 4 toabout 16. The HLB index is well known in the chemical arts and is ascale which measures the balance between the hydrophilic and lipophilicsolution tendencies of a compound. The HLB scale ranges from 1 toapproximately 50, with the lower numbers representing highly lipophilictendencies and the higher numbers representing highly hydrophilictendencies.

Suitable non-ionic surfactant families include acetylenic diols such asthose sold under the trade name Surfynol® manufactured and sold by AirProducts, Inc. Additional examples of acetylenic diols include:2,4,7,9-tetramethyl-5-decyne-4,7-diol;2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate (1.75 EO/OH);2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate (5 EO/OH);2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate (15 EO/OH); andmixtures of the acetylenic diols thereof. Such acetylenic diols areavailable from Aldrich Chemical Co., Milwaukee, Wis.

Another family of acceptable non-ionic surfactants includes theethoxylate fatty alcohols, which can generally be represented by theformula R¹—(CH₂CH₂O)_(n)—R²; wherein R¹ is a C₆ or higher linear,branched or substituted alkyl group, “n” is an integer from 1 to 40 andR² is H or a C₁-C₄ alkyl group. Examples of suitable surfactants in thiscategory include those manufactured and sold by Dow Chemical, Midland,Mich. under the trade name Tergitol® such as Tergitol TMN-6; TergitolTMN-3 and Tergitol TMN-10.

Water-soluble silicone glycols may also be used as a non-ionicsurfactant for purposes of this invention. Such materials are widelyknown in the art for use as surfactants and wetting agents. The siliconeglycols or silicone polyethers will have a general formula of:

wherein “x” and “y” are integers≧0 and “z” is an integer>0. The moleratio of “x” to (x+y+z) can be from about 0 percent to about 95 percent.The ratio of “y” to (x+y+z) can be from about 0 percent to about 25%.The R⁰-R⁹ moieties can be independently any organofunctional groupincluding C₁ or higher alkyl groups, ethers, polyethers, polyesters,amines, imines, amides, or other functional groups including the alkyland alkenyl analogues of such groups or hydrogen or hydroxyl. The R¹⁰moiety is an amino functional moiety including but not limited toprimary amine, secondary amine, tertiary amines, quaternary amines,unsubstituted amides and mixtures thereof. An exemplary R¹⁰ moietycontains one amine group per constituent or two or more amine groups persubstituent, separated by a linear or branched alkyl chain of C₁ orgreater. R¹¹ is a polyether functional group having the generic formula:—R¹²—(R¹³—O)_(a)—(R¹⁴O)_(b)—R¹⁵, wherein R¹², R¹³, and R¹⁴ areindependently C₁₋₄alkyl groups, linear or branched; R¹⁵ can be H or aC₁₋₃₀ alkyl group; and “a” and “b” are integers of from 1 to about 100,more specifically from about 5 to about 30. R¹¹ groups may also containamine, amide, carboxyl or other functionality within or attached to thepolyether substituent. Exemplary silicone polyethers include DC-2501 andQ2-5211 manufactured and sold by Dow Corning, Midland, Mich., Rhodasil®SP3300 PEX and Rhodasil Surfactant 5193 Manufactured and sold by Rhodia,Inc., and SF-1488 manufactured and sold by GE Silicones.

An especially interesting class of polyether polysiloxanes are theamino-funcitonal polyether polysiloxanes. Exemplary aminofunctionalpolyether polysiloxanes are the Wetsoft CTW family manufactured and soldby Wacker, Inc. Other exemplary polysiloxanes can be found in U.S. Pat.No. 6,432,270 by Liu, et.al. These amino-functional polyethers are foundto be capable of substantially increasing the surface feel of theproduct. Hence, use of such materials can simultaneously increase thetransfer efficiency of the surfactant/deliquescent salt solution to thetissue sheet while further increasing the surface softness of theproduct.

Combinations of silicone surfactants with non-ionic, non-siliconesurfactants can also be used.

Additional chemical additives, such as permanent wet strength agents,may be applied to the sheets provided their use is not antagonistic tothe desired results. It is necessary to avoid a reaction that wouldcause precipitation of one or more components of the deliquescentmaterial that would render the material no longer being deliquescent.For example, with calcium chloride, the interaction with sodiumcarbonate would cause precipitation of calcium carbonate with formationof the non-deliquescent compound sodium chloride. Hence, the resultingsheet would no longer be capable of a high equilibrium moisture content.

The tissue products of this invention can have one, two, three or moretissue sheets or plies containing non-ionic surfactants and deliquescentsalts. The tissue sheets can be positioned in different ways to deliverthe desired benefits. For example, for a three-ply product, the twoouter plies can contain a non-ionic surfactant and a deliquescent saltwhile the inner ply does not. For a two-ply product, it is advantageousthat both plies contain a non-ionic surfactant and a deliquescent salt.For a single-ply product, the non-ionic surfactant and the deliquescentsalt can be applied to one or both outer surfaces of the ply.

As used herein, a “tissue” sheet is any low density cellulosic sheetuseful for tissue products and having a dry sheet bulk of 2 cubiccentimeters or greater per gram, more specifically about 3 cubiccentimeters or greater per gram, more specifically about 5 cubiccentimeters or greater per gram, more specifically about 10 cubiccentimeters or greater per gram, more specifically from about 5 to about25 cubic centimeters per gram, and still more specifically from about 10to about 20 cubic centimeters per gram. Excluded are relatively highdensity sheets commonly used as writing papers and the like.Particularly suitable tissue sheets include cellulosic sheets useful forfacial tissues, bath tissues, paper towels, table napkins and the like.The “dry sheet bulk” is calculated as the quotient of the “dry sheetcaliper” (hereinafter defined) of a sheet, expressed in microns, dividedby the dry basis weight, expressed in grams per square meter. Theresulting dry sheet bulk is expressed in cubic centimeters per gram.More specifically, the dry sheet caliper is the representative thicknessof a single sheet measured in accordance with TAPPI test methods T402“Standard Conditioning and Testing Atmosphere For Paper, Board, PulpHandsheets and Related Products” and T411 om-89 “Thickness (caliper) ofPaper, Paperboard, and Combined Board” with Note 3 for stacked sheets.The micrometer used for carrying out T411 om-89 is an Emveco 200-ATissue Caliper Tester available from Emveco, Inc., Newberg, Oreg. Themicrometer has a load of 2 kilo-Pascals, a pressure foot area of 2500square millimeters, a pressure foot diameter of 56.42 millimeters, adwell time of 3 seconds and a lowering rate of 0.8 millimeters persecond.

As used herein, the “equilibrium moisture content” represents themoisture content of the tissue sheet at 50% relative humidity and 25° C.(standard TAPPI conditions). At equilibrium, the amount of moisturewithin the sheet will not change with time at the same humiditycondition. The equilibrium moisture content is expressed as a weightpercent of the dry sheet including the deliquescent material and anyadditional non-volatile components. More specifically, the dry samplesheets should be conditioned at least 4 hours at the TAPPI standardconditions prior to determining the equilibrium moisture content of thesheet. The equilibrium moisture content in the sheet can be controlledby the absorbent capacity of the sheet, the amount of water on a percentbasis that the deliquescent material absorbs, the amount of deliquescentmaterial in the sheet and the amount of non-ionic surfactant added.

As used herein, the “Single Water Drop Test” is used to determine thehydrophilicity of a tissue sheet and characterize the effectiveness ofthe surfactant/deliquescent salt solution. The “Single Water Drop Test”is performed on the equilibrated substrate to which thesurfactant/deliquescent salt solution is to be applied. The substrate isconditioned for a minimum of 4 hours at 23.0° C.±2.0° C. and a relativehumidity of 50%±5%. The conditioned test sample is then placed on a dryglass plate. A single drop (100 microliters, 0.1±0.01 ml.) of theaqueous surfactant/deliquescent salt solution (23.0° C.±2.0° C.) isdispensed from an Eppendorf style pipet positioned slightly above thesurface of the test specimen. The drop should be positioned close to thecenter of the test specimen. The aqueous surfactant/deliquescent saltsolution drop is viewed by the naked eye on a plane horizontal to thesurface of the test specimen. A stopwatch is started immediately afterthe water drop is dispensed onto the test specimen. The elapsed time forthe water drop to be completely absorbed by the sample, measured inseconds, is the Single Water Drop Test value (wet out time) for thattest specimen. The water drop is completely absorbed when it completelydisappears, that is, there is no visible vertical element of the waterdrop remaining. To determine the Single Water Drop Test value for anygiven material, the foregoing procedure is carried out on threerepresentative equilibrated substrate sample sheets and the averagevalue from the three tests is the Single Water Drop Test value for thematerial. If, after 3 minutes, the water drop is not completelyabsorbed, the test is stopped and the Single Water Drop Test value isassigned a value of 180 seconds.

In the interests of brevity and conciseness, any ranges of values setforth in this specification contemplate all values within the range andare to be construed as written description support for claims recitingany sub-ranges having endpoints which are whole number values within thespecified range in question. By way of a hypothetical illustrativeexample, a disclosure in this specification of a range of from 1 to 5shall be considered to support claims to any of the following ranges:1-5; 1-4; 1-3; 1-2; 2-5; 2-4; 2-3; 3-5; 3-4; and 4-5. In addition, anyof the foregoing aspects of this invention can be further defined by anycombination of one or more of the specified values and ranges recitedfor any properties described herein.

EXAMPLES

For the applicable examples below, the equilibrium moisture content wasdetermined for tissue samples as follows:

Treated samples were placed in a 100° C. oven and air-dried for 1 hour.Sample sizes of 1-2 grams were selected, although larger or smallersizes can be used depending upon the degree of accuracy desired. A dry400 cc wide mouth jar with a screw cap was weighed and the weight (W₂)recorded to the nearest 0.001 gram. After drying, the tissue sample wasplaced immediately into the weighed-400 cc wide mouth jar and capped.Samples were allowed to cool to ambient temperature and the weight ofthe dry tissue sample and bottle (W₁) determined to the nearest 0.001gram. The bone dry weight of the tissue sample, (W_(d)), was thencalculated from the equation (W₁−W₂). The jars with sample were thenuncapped and placed in standard TAPPI conditions to equilibrate for 16hours. After equilibration time was complete, the jars were capped andthe weight of the conditioned tissue, jar and lid (W₃) recorded. Incases where air circulation into the container is an issue, it ispreferred to remove the dried samples from the sample jar and allow thesamples to equilibrate on a raised rack instead of within the container.After conditioning the sample is then returned to the jar, capped andweighed. The equilibrium moisture content (W_(e)) is then calculatedfrom the equation (W₃−W₁). The percent equilibrium moisture was thencalculated from the equation [(W_(e)/W_(d))*100].

Example 1

This example demonstrates the reduction in the Single Water Drop Testvalues by incorporating small amounts of a non-ionic surfactant into thesurfactant/deliquescent salt solution. Specifically, an aqueous solutionof magnesium chloride (MgCl₂) was prepared by dissolving 2.95 parts ofMgCl₂.6H₂0 in 1 part of distilled water at room temperature. This ratiogave a deliquescent salt solution having 35 percent by weight MgCl₂. Thesolution had a Single Water Drop Test value of 41 seconds when placed ona 3-ply creped, untreated, facial tissue basesheet.

For comparison, 20×10⁻³ ml of an non-ionic surfactant was added to 100parts of the concentrated magnesium chloride solution. The non-ionicsurfactant was, 2,4,7,9-tetramethyl-5-decene-4,7-diol ethoxylate (1.75EO/OH) obtained from Aldrich Chemical Co., Milwaukee, Wis. After mixing,when placed on the same 3-ply creped, untreated facial tissue basesheet,the resulting surfactant/deliquescent salt solution was found to have aSingle Water Drop Test value of about 4 seconds.

Examples 2 and 3

These comparative examples demonstrate the impact that the addition of asmall amount of non-ionic surfactant can have on speed and absorption ofthe deliquescent salt solution into a tissue product run on commercialmanufacturing equipment. For both Examples 2 and 3, a two-ply crepedtissue sheet having a finished basis weight of 15.0 pounds per 2880square feet and a furnish consisting of 65 percent hardwood and 35percent softwood fibers was used. Each ply was made from a stratifiedfiber furnish including two outer layers and a middle layer. Thedeliquescent salt solution was printed on both outer sides of the 2-plytissue product via a simultaneous offset rotogravure printing process.The salt solutions were delivered as aqueous solutions havingapproximately 42 percent solids. The gravure rolls were electronicallyengraved, chrome-over-copper rolls supplied by Southern GraphicsSystems, located at Louisville, Ky. The rolls had a line screen of 360cells per lineal inch and, a volume of 8 Billion Cubic Microns (BCM) persquare inch of roll surface. The rubber backing offset applicator rollshad a 75 Shore A durometer cast polyurethane surface and were suppliedby American Roller Company, located at Union Grove, Wis. The process wasset up to a condition having 0.375 inch interference between the gravurerolls and the rubber backing rolls and 0.003 inch clearance between thefacing rubber backing rolls. The simultaneous offset/offset gravureprinter was run at the speeds given in the examples.

For Example 2, a deliquescent salt solution of calcium chloride (CaCl₂)was prepared by mixing 100 parts of CaCl₂.6H₂0 with 20 parts of water togive a solution containing 42 percent by weight calcium chloride. Thedeliquescent salt solution was printed onto the two-ply tissue productdescribed above by passing it through the printer twice at a slow speedof 50 feet per minute. The resulting product contained 4.9 dry weightpercent calcium chloride and had an equilibrium moisture content of8.1%.

For Example 3, 500 ppm of Surfynol® 420 non-ionic surfactant from AirProducts, Inc. was added to the CaCl₂ solution used in Example 2. Theresulting surfactant/deliquescent salt solution was mixed for 5 minutesat room temperature using a standard mechanical mixer run a speed of 300rpm. The solution was found to have a Single Water Drop Test value ofless than 5 seconds. The same untreated two-ply tissue product describedabove was run through the printer twice, but at a much higher speed of200 feet per minute. The resulting tissue product contained 13.9 percentcalcium chloride and an equilibrium moisture content of 22.5%.

A comparison of Examples 2 and 3 illustrates the advantage of using anon-ionic surfactant to increase the amount of deliquescent saltretained by tissue product, even at higher speeds. Because of thegreater hydrophilicity of the non-ionic surfactant-containing solution,more solution is transferred from the printing cells to the tissuesheet, resulting in greater deliquescent salt add-on.

It will be appreciated that the foregoing description and examples,given for purposes of illustration, are not to be construed as limitingthe scope of this invention, which is defined by the following claimsand all equivalents thereto.

1. A tissue product comprising a tissue sheet containing a deliquescentsalt and a water-soluble non-ionic surfactant, said tissue sheet havingan equilibrium moisture content of from about 10 to about 30 dry weightpercent.
 2. The product of claim 1 wherein the deliquescent salt isselected from the group consisting of aluminates, calcium chloride,magnesium chloride, lithium chloride, sodium acetate, potassium acetate,ammonium acetate and trimethylamine n-oxide.
 3. The product of claim 1wherein the deliquescent material is lithium chloride.
 4. The product ofclaim 1 wherein the deliquescent material is calcium chloride.
 5. Theproduct of claim 1 wherein the deliquescent material is magnesiumchloride.
 6. The product of claim 1 wherein the non-ionic surfactant isan acetylenic diol.
 7. The product of claim 1 wherein the non-ionicsurfactant is an ethoxylated fatty alcohol.
 8. The product of claim 1wherein the non-ionic surfactant is a water-soluble silicone glycol. 9.The product of claim 1 wherein the non-ionic surfactant is a siliconepolyether.
 10. The product of claim 1 wherein the non-ionic surfactantis an amino-functional polyether polysiloxane.
 11. A method for treatinga tissue sheet comprising: (a) providing a dry tissue sheet; (b)preparing a surfactant/deliquescent salt solution containing about0.0001 dry weight percent or greater of a non-ionic surfactant and fromabout 20 to about 80 dry weight percent of a deliquescent salt; and c)topically applying the surfactant/deliquescent salt solution to thetissue sheet, wherein the equilibrium moisture content of the tissuesheet is increased.
 12. The method of claim 11 wherein the equilibriummoisture content of the tissue sheet is from about 10% to about 30% byweight of dry fibers.
 13. The method of claim 11 wherein the non-ionicsurfactant has an HLB value of about 4 or greater.
 14. The method ofclaim 11 wherein the surfactant/deliquescent salt solution is sprayedonto the surface of the sheet.
 15. The method of claim 11 wherein thesurfactant/deliquescent salt solution is printed onto the surface of thesheet.
 16. The method of claim 11 wherein the Water Drop Test value ofthe tissue sheet is about 12 seconds or less.
 17. The method of claim 11wherein the Water Drop Test value of the tissue sheet is about 8 secondsor less.
 18. The method of claim 11 wherein the Water Drop Test value ofthe tissue sheet is about 6 seconds or less.
 19. The method of claim 11wherein the Water Drop Test value of the tissue sheet is about 4 secondsor less.
 20. The method of claim 11 wherein the Water Drop Test value ofthe tissue sheet is about 1 second or less.
 21. The method of claim 11wherein the tissue sheet is traveling at a speed of about 100 feet orgreater per minute.